Could you, please, elaborate on it? What I really want to know, is how certain you are, that this is "dragging something", and not just cursor has activated effect (i.e. Resurrection spell was cast without explicit target), which makes a bit more sense to me?

I thought it would be for the glowing active spell cursor too. Then I thought it would be if the cursor was over something/someone you could right click to interact with. The only use I can think of is for a secure handler to check during it's OnClick to see if it should do it's OnDragStop instead.